Embodiments of the present invention relate to the regeneration of ion exchange resin with a regenerant solution and recovery of the spent regenerant solution.
Ion exchange resins are used to treat fluids that include gases and liquids to remove ions, contaminants, and dissolved solids. The resins can be used in many different types of separation, purification, and decontamination processes including water treatment, treatment of toxic liquids or gases, or other applications. The ion exchange resins can be in the form of organic polymer beads, membranes, or other structures, and can include (i) cation exchange resins which have functional groups that are strong or weak acid groups, and (ii) anion exchange resins which have functional groups which are strong or weak base groups. In a typical ion exchange resin system, the fluid to be treated is passed across or through the ion exchange resin. For example, well or tap water can be treated with an ion exchange resin to remove divalent or contaminant ions to provide softened or purified water. The ion exchange resin removes certain ions from the water and exchanges them for other ions in a reversible chemical reaction. For example, multivalent and divalent ions such as, for example, Ca+2, Mg+2, and SO4−2 ions, can be removed from the fluid being treated and exchanged for Na+ ions in the resin.
Besides water treatment, ion exchange resins can have many other applications. For example, in one application, ion exchange resins are used to remove poisonous metal (e.g., copper) and heavy metal (e.g., lead or cadmium) ions from a solution, and replace them with more innocuous ions, such as sodium and potassium. Ion exchange resins can also be used to remove organic contaminants from water; for example, using an activated charcoal filter to remove the chlorine mixed with anionic resin to remove organic contaminates. Still other ion exchange resins remove organic ions, such as MIEX (magnetic ion exchange) resins. Still other applications of ion exchange resin systems include the treatment of: salt water pre-treatment in desalination processes; industrial waste liquids and gases to remove hazardous ions and compounds; waste from nuclear power plants to remove radioactive or other toxic materials; fluids to recover valuable metals; industrial drying of gases; food industry applications such as wine-making and sugar manufacture; medical applications that include the development and preparation of drugs and antibiotics, such as streptomycin and quinine; treatments for ulcers, TB, kidneys, and other organs; and the prevention of coagulation of blood and dextrose. Ion exchange processes can be used to separate and purify metals, including separating uranium from plutonium and other actinides, such as thorium, lanthanum, neodymium, ytterbium, samarium, and lutetium, from each other and the other lanthanides. Ion exchange resins can also be used to catalyze organic reactions, such as in self-condensation reactions. Ion exchange resins are also used in the manufacture of fruit juices (e.g., orange juice) where they are used to remove bitter-tasting components and so improve the flavor. In the processing of sugar, ion exchange resins are used to convert one type of sugar into another type of sugar and to decolorize and purify sugar syrups. Ion exchange resins are also used in the manufacturing of pharmaceuticals, not only for catalyzing certain reactions but also for isolating and purifying pharmaceutical active ingredients.
In any of these applications, after a number of treatment cycles, the used ion exchange resin becomes spent or exhausted and needs to be regenerated to remove the ions which have exchanged into, and accumulated in, the spent resin. Ion exchange resins contain a finite number of ion exchange sites, and the exchange capacity of the resins eventually becomes spent as the resins become saturated with ions extracted from a fluid. An ion exchange resin can also lose its efficiency from plugging up with solids, such as sand or other particles, which are present in the liquid being treated.
To regenerate the spent ion exchange resin, the spent resin is treated with a resin regenerant solution containing ions that exchange with the accumulated ions in the resin to recharge the resin. The composition of the regenerant solution depends on the chemical composition of the ion exchange resin and type of ions accumulated in the resin. For example, spent cation exchange resin can be treated by soaking the resin in a regenerant solution comprising sodium chloride or potassium dissolved in water to remove accumulated divalent ions and solids. The sodium or potassium ions replace divalent ions such as calcium and magnesium which are trapped in the ion exchange resin with sodium ions. Ion exchange resins can also be regenerated with solutions comprising other forms of chloride ions, such as hydrochloric acid. Oftentimes, after regeneration, the ion exchange resin can be rinsed with fresh water or other liquids to displace residual regenerant solution. The regenerant solution and rinse liquid both contain dissolved divalent ions which contaminate the regenerant solution and prevent its reuse. Similarly, spent anion exchange resins can also be treated with other types of regenerant solutions and/or rinse liquids which also accumulate in the spent resins.
The disposal of spent regenerant solutions and rinse liquids into municipal wastewater systems creates environmental problems and increases regeneration process costs. Municipal wastewater plants often cannot remove all of the mineral hardness compounds, such as sodium chloride, from the incoming water stream, and thus, these compounds are passed out with the processed water into the environment to contaminate rivers, lakes and seas, or even ground water and surrounding land, with undesirable metallic ions. Also, the higher concentrations of total dissolved salts in processed water, such as chloride, sodium and boron ions in particular, limit reuse of such water in farming and agricultural applications. The contribution to municipal sewage of salt water discharge from household ion exchange systems has reached such major proportions that regulations are being promulgated on the reduction of salt use in the regeneration of ion exchange resins and prohibiting the discharge of brines to municipal sewage systems. For example, the discharge of salt solutions from ion exchange processes used in food, tanning and textile industries, and hospitals through municipal wastewater systems can exceed thousands of tons of salt per year. Also, disposal of spent regenerant solutions into the wastewater systems creates a need for additional chemicals and fresh water to form new regenerant solution, further increasing the costs associated with regenerating exchange resins.
For reasons including these and other deficiencies, and despite the development of various ion exchange regeneration systems, apparatus, and methods, further improvements in the treatment of spent regenerant solution and other waste liquids generated in the process of regenerating ion exchange resins are continuously being sought.